A basic wireless power transfer system may include a wireless power transmitter unit (PTU) and a wireless power receiving unit (PRU). A PRU may be implemented in a mobile computing device, such as a laptop, tablet or smart phone, which can be placed on a charging mat equipped with a PTU. The PTU may include a transmit (Tx) coil and a PRU may include a receive (Rx) coil. In typical wireless power transfer systems, the transmit coil creates an alternating electromagnetic field and the receive coil takes power from the electromagnetic field and converts it back into electrical current to charge the battery and/or power the device.
Two common techniques for wireless power transfer are referred to as inductive charging and magnetic resonance charging. In inductive charging, the transmit and receive coils are tightly coupled and operate like two windings of a transformer. In magnetic resonance charging, the transmit and receive coils are loosely coupled and both coils are tuned to the same resonant frequency to improve efficiency. In some circumstances, the electromagnetic field generated by the transmit coil may be transmitted to areas that are outside of the wireless charging area. This energy is wasted and may interfere with other electronic components.
The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the 100 series refer to features originally found in FIG. 1; numbers in the 200 series refer to features originally found in FIG. 2; and so on.